Enhanced oil recovery methods using a fluid containing a sacrificial agent

ABSTRACT

A method and a system for producing petroleum from a formation utilizing a sacrificial agent and a surfactant are provided. The sacrificial agent reduces the amount of surfactant required to enhance oil recovery from a petroleum-bearing formation. The sacrificial agent is provided in a oil recovery formulation comprising a sacrificial agent and a surfactant dispersed in a fluid. The sacrificial agent is selected from the group consisting of a compound comprising a single carboxylic acid, a single carboxylic acid derivative, or a single carboxylate salt, or a compound lacking a carboxylic acid group, a carboxylate group, a sulfonic acid group, or a sulfonate group that is a pheol, a sulphonamide, or a thiol, or a compound having a molecular weight of 1000 or less that comprises one or more hydroxyl groups. The oil recovery formulation is introduced into a petroleum-bearing formation and petroleum is produced therefrom.

This present application claims the benefit of U.S. Patent ApplicationNo. 61/679,180, filed Aug. 3, 2012.

FIELD OF THE INVENTION

The present invention is directed to methods for recovering petroleumfrom a formation, and, in particular, the present invention is directedto methods of enhanced oil recovery using a surfactant.

BACKGROUND OF THE INVENTION

Production of petroleum from a formation can be characterized by atleast three different stages of production. During primary production,innate driving forces within the formation are sufficient to drive thepetroleum from the formation, such as from the depths of a subterraneanformation to the earth's surface. Innate driving forces may includenatural pressure-generation mechanisms within the formation such as, forexample, downward water displacement, natural gas expansion, andgravity-induced drainage within a well. At some point, the innatedriving forces may decrease to such a degree that productionsignificantly wanes or stops. In secondary production, an externallyapplied force may be supplied to the formation to provide sufficientenergy to remove the petroleum therefrom. The externally applied forcemay include, for example, an injected fluid that creates fluid pressurethat supplements or replaces that of the innate driving forces withinthe formation. External lifting mechanisms such as pumps may also beused to assist in production of the petroleum.

After secondary production no longer produces sufficient petroleum to beeconomically viable, there may, in many instances, still be substantialresidual petroleum within the formation. Insufficient mobility of thepetroleum within the formation may be one of the causes leading to itsretention. Mobility of petroleum within a formation may be related tothe innate viscosity of the petroleum, interfacial tension between thepetroleum and the formation, combinations thereof, and the like. Intertiary production, also referred to as enhanced oil recoverytechniques, the mobility of petroleum within the formation is altered insome manner, thereby inducing mobilization and production of thepetroleum to take place. Techniques for altering the mobility of thepetroleum within the formation may include heating the petroleum toreduce its viscosity, introducing a miscible fluid such as carbondioxide or a hydrocarbon to the petroleum to reduce its viscosity, orintroducing a fluid containing a surfactant to the formation to reducethe interfacial tension between the petroleum and the formation.Although it was once conventional to conduct enhanced oil recoverytechniques following the completion of primary and secondary production,it is now common to employ these techniques at any point during aproduction operation. That is, enhanced oil recovery techniques may beemployed during primary or secondary production or as a separateproduction operation.

One problem that may be frequently encountered when lowering theinterfacial tension within a formation using a surfactant is that ofexcessive surfactant sorption to the surface of the formation. As usedherein, the term “sorption” collectively refers to absorption,adsorption, or any combination thereof. Excessive surfactant sorption tothe formation may limit the surfactant's ability to reduce interfacialtension within a desired region of the formation. Although additionalsurfactant can be introduced to the formation to offset that renderedineffective by sorption, such an approach may be undesirable from aneconomic standpoint, since many surfactants can be relatively costly.For at least this reason, it is ordinarily desirable to limit the amountof surfactant used during enhanced oil recovery production.

To address surfactant sorption within a formation, sacrificial agentsare often used in conjunction with a surfactant. As used herein, theterm “sacrificial agent” refers to a substance that mitigates thesorption of a surfactant to a formation or otherwise reduces theretention of the surfactant within the formation. Without limitation orbeing bound by theory or mechanism, the sacrificial agent may modify thesurface of the formation or itself be sorbed to the formation such thatsorption of the surfactant is reduced or eliminated. Ideally, thesacrificial agent is less costly than the surfactant, thereby allowingbetter process economics to be realized. Commonly used sacrificialagents may include, for example, inorganic salts, water-soluble polymerviscosifiers, lignosulfonates, cellulose and cellulose derivatives,starch and starch derivatives, and polybasic carboxylic acids,particularly chelating acids. Chelating acids may be particularlyadvantageous in this regard, since they may chelate metal ions, such ascalcium and magnesium, that may react with surfactants and render themineffective for reducing the interfacial tension within a formation.

SUMMARY OF THE INVENTION

In one aspect, the present invention is directed to a method forrecovering petroleum comprising:

providing an oil recovery formulation comprising a fluid, a surfactantdispersed in the fluid, and a sacrificial agent dispersed in the fluid,wherein the sacrificial agent is selected from the group consisting of acompound comprising a single carboxylic acid, a single carboxylic acidderivative, or a single carboxylate salt; a compound lacking acarboxylic acid group, a carboxylate group, a sulfonic acid group, and asulfonate group that is a phenol, a sulfonamide, or a thiol; a compoundhaving a molecular weight of 1000 or less and comprising one or morehydroxyl groups; and mixtures thereof;

introducing the oil recovery formulation into a petroleum-bearingformation;

contacting the oil recovery formulation with the petroleum-bearingformation and with petroleum in the petroleum-bearing formation; and

producing petroleum from the petroleum-bearing formation afterintroducing the oil recovery formulation into the petroleum-bearingformation.

In another aspect, the present invention is directed to an oil recoverycomposition comprising,

-   -   a fluid;    -   a sacrificial agent selected from the group consisting of a        compound comprising a single carboxylic acid, a single        carboxylic acid derivative, or a single carboxylate salt; a        compound lacking a carboxylic acid group, a carboxylate group, a        sulfonic acid group, and a sulfonate group that is a phenol, a        sulfonamide, or a thiol; a compound having a molecular weight of        1000 or less and comprising one or more hydroxyl groups; and        mixtures thereof, wherein the sacrificial agent is dispersed in        the fluid; and    -   a surfactant.

In another aspect, the present invention is directed to a system,comprising an oil recovery formulation comprising a fluid, a surfactantdispersed in the fluid, and a sacrificial agent dispersed in the fluid,wherein the sacrificial agent is selected from the group consisting of acompound comprising a single carboxylic acid, a single carboxylic acidderivative, or a single carboxylate salt; a compound lacking acarboxylic acid group, a carboxylate group, a sulfonic acid group, and asulfonate group that is a phenol, a sulfonamide, or a thiol; a compoundhaving a molecular weight of 1000 or less and comprising one or morehydroxyl groups; and mixtures thereof;

-   -   a petroleum-bearing formation;    -   a mechanism for introducing the oil recovery formulation into        the petroleum-bearing formation; and    -   a mechanism for producing petroleum from the petroleum-bearing        formation subsequent to introduction of the oil recovery        formulation into the formation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustration of a petroleum production system in accordancewith the present invention.

FIG. 2 is a diagram of a well pattern for production of petroleum inaccordance with a system and process of the present invention.

FIG. 3 is a diagram of a well pattern for production of petroleum inaccordance with a system and process of the present invention.

FIGS. 4 and 5 respectively show illustrative retention plots of variousfluid components in the presence and absence of erythorbic acid.

FIG. 6 shows an illustrative production chart for an oil recovery floodin which erythorbic acid was added to an ASP slug.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed to methods for recovering petroleumfrom a formation, and, in particular, the present invention is directedto methods of enhanced oil recovery using a surfactant. Morespecifically, the present invention is directed to methods of enhancedoil recovery using an oil recovery formulation comprising a surfactantand a sacrificial agent, where the sacrificial agent may comprise asingle carboxylic acid, carboxylic acid derivative, or carboxylate salt;or an acidic substance or salt of an acidic substance that lacks acarboxylic acid, sulfonic acid, or a salt thereof; or a compound havinga molecular weight of about 1000 or less and having one or more hydroxylgroups.

As discussed above, a number of different types of sacrificial agentshave been used in conjunction with the introduction of surfactants to apetroleum-bearing formation, particularly during enhanced oil recoveryoperations. Although these sacrificial agents have been used withvarying degrees of success, the discovery and development of newsacrificial agents may be desirable to increase operational flexibilityfor a given application, to reduce costs associated with the surfactantand/or the sacrificial agent, and/or to increase the amount of petroleumproduced from the formation.

When a petroleum-bearing formation is in its native environment (e.g.,in a subterranean formation), the formation may be in a reduced state.When removed from its native environment, such as in a core sampleobtained from the formation for oil recovery studies, oxidation mayoccur, thereby changing the oxidative state of the core sample and itsproperties. To return the core sample to a reduced state that may bemore like that natively present within a subterranean formation, thecore sample may be treated with a reducing agent before conductingtesting further thereon. Sodium dithionite is often used for thispurpose.

In enhanced oil recovery operations, an oil recovery formulationcontaining a polymer and a surfactant may be utilized to enhance oilrecovery from a formation. An alkali may often be present as well. Thesetwo types of enhanced oil recovery operations are commonly referred toas surfactant-polymer (SP) and alkali-surfactant-polymer (ASP) floods,respectively. In the process of testing an ASP flood on a sodiumdithionite-reduced core sample, polymer degradation was observed, whichwas believed to be promoted by the sodium dithionite. Accordingly, thecore sample reduction was conducted using erythorbic acid, which is amilder reducing agent, followed by an ASP core flood. Surprisingly,treatment of the core sample with erythorbic acid significantlydecreased retention of the surfactant within the core sample. Althoughproviding the desired core reduction, sodium dithionite, in contrast,did not significantly impact retention of the surfactant within the coresample.

The present invention is directed to a process, a system, and acomposition for enhanced oil recovery from a petroleum-bearingformation. The oil recovery formulation composition of the presentinvention comprises a surfactant and a sacrificial agent having one ormore chemical structural attributes of erythorbic acid. The oil recoveryformulation may also include a polymer and/or a basic compound. Thesacrificial agent is effective to decrease retention of the surfactantin the petroleum-bearing formation. The process of the present inventionutilizes the oil recovery formulation composition and the system of thepresent invention to produce petroleum from a petroleum-bearingformation. The oil recovery formulation is introduced into apetroleum-bearing formation and is contacted with petroleum in thepetroleum-bearing formation. Petroleum is produced from thepetroleum-bearing formation subsequent to contacting the oil recoveryformulation with petroleum in the petroleum-bearing formation. In apreferred embodiment, the oil recovery formulation comprises asurfactant and erythorbic acid.

The oil recovery formulation composition comprises a sacrificial agenthaving one or more chemical structural attributes of erythorbic acid.The structure of erythorbic acid is shown below in Formula 1. Erythorbicacid is an enantiomer of ascorbic acid, also known as Vitamin C, whichshown in Formula 2, and ascorbic acid may function as a sacrificialagent in a like manner to erythorbic acid.

As putative sacrificial agents, erythorbic acid and ascorbic acidcontain several chemical structural features, any of which, separatelyor together, may contribute to a surprising decrease of surfactantretention within a formation to which the oil recovery formulation hasbeen introduced. Erythorbic acid and ascorbic acid contain both neutralalcohol-type hydroxyl groups and enol-type hydroxyl groups, the latterof which confer acidity to the compounds. Erythorbic acid and ascorbicacid also contain considerably fewer hydroxyl groups than carbohydrate-and starch-based sacrificial agents that have been previously used inthe art. The enol-type hydroxyl groups of erythorbic and ascorbic acids'reductone structures may also be readily oxidized to a diketone, therebyallowing erythorbic acid and ascorbic acid to function as mild reducingagents. The oxidation products of erythorbic acid and ascorbic acid,dehydroerythorbic acid and dehydroascorbic acid, respectively, may alsoplay a role in decreasing surfactant retention within apetroleum-bearing formation. These compounds are shown in Formulas 3 and4, respectively. In addition, erythorbic acid and ascorbic acid mayundergo lactone hydrolysis under formation temperature and pressureconditions within a petroleum-bearing formation to liberate a freecarboxylic acid, which may also contribute to reducing the surfactantretention.

In addition to the above features, erythorbic acid and ascorbic acid mayform weakly bound chelates with metal ions. Without being bound bytheory or mechanism, it is believed that chelation of the sacrificialagent to a formation surface to permanently block a potential surfactantbinding site may play only a minor role in their function as sacrificialagents, given their fairly weak chelation properties, although weakchelation of the sacrificial agent with the formation surface mayinhibit binding of a surfactant to the formation surface for the periodof time until the sacrificial agent releases from the formation surface.It is believed that erythorbic acid and ascorbic acid may bedistinguished from polybasic carboxylic acid chelation agents since theylack a free carboxylic acid group for metal ion chelation. Even in theirhydrolyzed form, they still lack a second carboxylic acid group neededfor strong metal ion chelation to take place.

In one aspect, the oil recovery formulation may comprise a sacrificialagent compound comprising a single carboxylic acid, carboxylic acidderivative, or carboxylate salt moiety. As used herein, the term“carboxylic acid derivative” refers to a compound containing a reactionproduct of a carboxylic acid moiety that does not retain a freecarboxylic acid hydroxyl group. Illustrative carboxylic acid derivativesinclude esters and amides, which may comprise a lactone or a lactam. Thesacrificial agent compound containing a single carboxylic acid moiety,carboxylic acid derivative moiety, or carboxylate salt moiety may alsocontain one or more hydroxyl groups.

The sacrificial agent of the oil recovery formulation may comprise amonocarboxylic acid compound or a salt thereof. As used herein, the term“monocarboxylic acid compound” refers to a compound containing only onecarboxylic acid group or carboxylate group. The monocarboxylic acidcompound of the sacrificial agent may be a hydrocarbon comprising 10carbons or fewer, or 9 carbons or fewer, or 8 carbons or fewer, or 7carbons or fewer, or 6 carbons or fewer, or 5 carbons or fewer. Themonocarboxylic acid compound may contain from 2-10 carbons, or from 3-9carbons, or from 4-8 carbons. The monocarboxylic acid compound maycomprise a straight carbon chain or may comprise a branched carbonchain. The monocarboxycylic acid compound may comprise a non-aromaticcyclic carbon ring, optionally with branching, or may comprise anaromatic ring, optionally with branching. The carbon chain or ring maycontain one or more heteroatoms selected from the group consisting ofoxygen, nitrogen, and sulfur within the chain or ring.

The monocarboxylic acid compound of the sacrificial agent may be ahydroxycarboxylic acid compound comprising one or more hydroxyl groups.The hydroxycarboxylic acid compound may comprise a straight carbon chainor a branched carbon chain. The hydroxycarboxylic acid compound maycomprise a non-aromatic cyclic carbon ring or an aromatic cyclic carbonring, optionally with branching. The carbon chain or ring may compriseone or more heteroatoms selected from the group consisting of oxygen,sulfur, and nitrogen within the chain or ring. Hydroxycarboxylic acidcompounds suitable for use as a sacrificial agent compound of the oilrecovery formulation may include from 1 to 10 hydroxyl groups, or from 1to 6 hydroxyl groups, or from 1 to 3 hydroxyl groups. The sacrificialagent may comprise a compound that is a monohydroxycarboxylic acid, adihydroxycarboxylic acid, a trihydroxycarboxylic acid, atetrahydroxycarboxylic acid, a pentahydroxycarboxylic acid, a saltthereof, or any combination thereof. The sacrificial agent may comprisea compound that is an α-hydroxycarboxylic acid, a β-hydroxycarboxylicacid, a γ-hydroxycarboxylic acid, a δ-hydroxycarboxylic acid, anε-hydroxycarboxylic acid, a salt thereof, or any combination thereof.

The sacrificial agent of the oil recovery formulation may comprise acompound comprising an enol or that is enolizable, including stabilizedenols. In some embodiments, the enol may only form as a transienttautomer where the enol may not persist as an abundant and observablespecies. As used herein, the term “stabilized enol” refers to a compoundcontaining a hydroxyl group bound to a doubly-bonded carbon in which atleast some of the enol tautomer persists as an abundant and observablespecies. Compounds such as β-diketones, β-ketoesters, and some acyloinsmay produce a stabilized enol. Reductones are another class of compoundsthat may produce a stabilized enol. As used herein, the term “reductone”refers to a compound having an enediol functionality located adjacent toa carbonyl group. Suitable reductone compounds may be straight chain,branched, or cyclic. Reductone compounds that may be used as thesacrificial agent or a portion thereof may have a structure as definedby Formula 5 below, wherein R₁ and R₂ comprise a carbon-containing grouphaving between 1 and 10 carbon atoms and R₁ and R₂ are the same ordifferent. Reductone compounds that may be used as the sacrificial agentor a portion thereof may have a structure as defined by Formula 6 below,wherein Z is O, NR₃, or CR₄R₅ and A comprises a divalentcarbon-containing group having between 1 and 10 carbon atoms. R₃ may beselected from H and a carbon-containing group having between 1 and 10carbon atoms, and R₄ and R₅ are independently selected from H and acarbon containing group having between 1 and 10 carbon atoms. Thesacrificial agent may comprise a reductone selected from the groupconsisting of erythorbic acid, ascorbic acid, reductic acid (A=CH₂ andZ=CH₂), a salt thereof, and any combination thereof.

In another aspect, the sacrificial agent of the oil recovery formulationmay be a compound that is acidic or is a salt thereof where the compoundlacks a carboxylic acid moiety, a sulfonic acid moeity, a carboxylatesalt moiety, or a sulfonate salt moiety. Such acidic compounds and saltsthereof include phenols, sulfonamides, and thiols.

In a further aspect, the oil recovery formulation may comprise asacrificial agent wherein the sacrificial agent comprises a compoundhaving a molecular weight of about 1000 or less comprising one or morehydroxyl groups. The sacrificial agent may comprise a compound havingone or more hydroxyl groups and have a molecular weight of 500 or less,or 300 or less, or 200 or less. The sacrificial agent may comprise acompound containing only one hydroxyl group, or containing only twohydroxyl groups, or containing only three hydroxyl groups, or containingonly four hydroxyl groups, or containing only five hydroxyl groups, orcontaining only six hydroxyl groups. At least a portion of the hydroxylgroups in a sacrificial agent compound containing hydroxyl groups may beenolic hydroxyl groups.

The sacrificial agent may be comprised of a carbohydrate. Suitablecarbohydrates include monosaccharides and low molecular weightoligosaccharides having a molecular weight of 1000 or less. Thesacrificial agent may comprise a compound selected from the groupconsisting of a monosaccharide, a disaccharide, a trisaccharide, atetrasaccharide, a pentasaccharide, and any combination thereof. Thecarbohydrate may comprise at least one reducing sugar or a derivativethereof. Suitable reducing sugars include, but are not limited to,glucose, glyceraldehyde, galactose, lactose, maltose, and fructose.

In another aspect, the oil recovery formulation may comprise asacrificial agent that is a compound comprising an oxidizable functionalgroup. In some embodiments, the sacrificial agent compound may be a“reducing acid”, a salt thereof, or a derivative thereof. As usedherein, a “reducing acid” refers to an acidic compound, a salt thereof,or a derivative thereof including esters, lactones, amides, and lactams,that contains a functional group that may undergo oxidation. The oilrecovery formulation may comprise two or more sacrificial agentcompounds wherein the compounds are a combination of an oxidizablecompound and its oxidation product(s), for example, a combination oferythorbic acid and dehydroerythorbic acid, salts, and derivativesthereof, or a combination of ascorbic acid and dehydroascorbic acid,salts, and derivatives thereof. In embodiments in which one or more ofthe sacrificial agent compounds comprise an oxidizable functional group,the methods described herein may further comprise oxidizing thesacrificial agent compound(s) after contacting the oil recoveryformulation with the formation.

The oil recovery formulation also comprises a surfactant in addition tothe sacrificial agent. The surfactant may an anionic surfactant. Theanionic surfactant may be a sulfonate-containing compound, asulfate-containing compound, a carboxylate compound, a phosphatecompound, or a blend thereof. The anionic surfactant may be an alphaolefin sulfonate compound, an internal olefin sulfonate compound, abranched alkyl benzene sulfonate compound, a propylene oxide sulfatecompound, an ethylene oxide sulfate compound, an ethyleneoxide-propylene oxide sulfate compound, or a blend thereof. The anionicsurfactant may contain from 12 to 30 carbons, or from 12 to 20 carbons.The surfactant of the oil recovery formulation may comprise an internalolefin sulfonate compound containing from 15 to 18 carbons or apropylene oxide sulfate compound containing from 12 to 15 carbons, or ablend thereof, where the blend contains a volume ratio of the propyleneoxide sulfate to the internal olefin sulfonate compound of from 1:1 to10:1.

The oil recovery formulation further comprises a fluid in which thesurfactant and the sacrificial agent are dispersed. The fluid may bewater or an aqueous brine, and the oil recovery formulation may be anaqueous mixture of the surfactant and the sacrificial agent. The fluidmay be comprised of water and a co-solvent. The co-solvent may be awater miscible organic solvent including water miscible alcohols,glycols, aldehydes, and ketones. The co-solvent may be methanol,ethanol, isopropanol, isobutyl alcohol, secondary butyl alcohol, n-butylalcohol, t-butyl alcohol, diethylene glycol butyl ether (DGBE),triethylene glycol butyl ether (TEGBE), sodium dihexyl sulfosuccinate(MA-80), ethylene glycol, acetone, or a combination thereof.

The fluid of the oil recovery formulation may be an aqueous brinesolution derived from the petroleum-bearing formation or formulated tohave a salt composition similar to an aqueous formation brine. In apreferred embodiment, the fluid of the oil recovery formulation is anaqueous brine solution produced from the petroleum-bearing formation.

The concentration of the surfactant in the oil recovery formulation mayrange from 0.05 wt. % to 5 wt % of the oil recovery formulation. Theconcentration of the surfactant in the oil recovery formulation mayrange from 0.1 wt. % to 3 wt. % or from 0.2 wt % to 1 wt. %, or from 0.3wt. % to 0.7 wt. % of the oil recovery formulation.

The concentration of the sacrificial agent in the oil recoveryformulation may range from 0.001 wt. % to 5 wt. % of the oil recoveryformulation. The concentration of the sacrificial agent in the oilrecovery formulation may range from 0.005 wt. % to 1 wt. %, or from 0.01wt. % to 0.5 wt. %, or from 0.05 wt. % to 0.1 wt. % of the oil recoveryformulation.

The oil recovery formulation comprising the surfactant, the sacrificialagent, and the fluid may further comprise a polymer dispersable in thefluid, and preferably soluble in the fluid, and the oil recoveryformulation comprising the surfactant, the sacrificial agent, the fluidand the polymer may further comprise an alkali as an aid for dispersingthe polymer in the fluid. The sacrificial agent may be used inconjunction with both SP and ASP enhanced oil recovery techniques.

The oil recovery formulation may comprise a polymer selected from thegroup consisting of polyacrylamides, partially hydrolyzedpolyacrylamides, polyacrylates, ethylenic co-polymers, biopolymers,carboxymethylcelloluses, polyvinyl alcohols, polystyrene sulfonates,polyvinylpyrrolidones, AMPS (2-acrylamide-methyl propane sulfonate), andcombinations thereof. Examples of ethylenic co-polymers includeco-polymers of acrylic acid and acrylamide, acrylic acid and laurylacrylate, and lauryl acrylate and acrylamide. Examples of biopolymersinclude xanthan gum, guar gum, alginic acid, and alginate salts.

The quantity of polymer in the oil recovery formulation, if any, shouldbe sufficient to drive a mixture of the oil recovery formulation andpetroleum through a petroleum bearing formation. The quantity of thepolymer in the oil recovery formulation may be sufficient to provide theoil recovery formulation with a dynamic viscosity at formationtemperatures on the same order of magnitude, or a greater order ofmagnitude, as the dynamic viscosity of petroleum in a petroleum-bearingformation at formation temperatures so the oil recovery formulation maypush a mixture of oil recovery formulation and petroleum through theformation. The quantity of the polymer in the oil recovery formulationmay be sufficient to provide the oil recovery formulation with a dynamicviscosity of at least 10 mPa s (10 cP), or at least 100 mPa s (100 cP),or at least 500 mPa s (500 cP), or at least 1000 mPa s (1000 cP) at 25°C. or at a temperature within a formation temperature range. Theconcentration of polymer in the oil recovery formulation may be from 250ppm to 5000 ppm, or from 500 ppm to 2500 ppm, or from 1000 to 2000 ppm.

The molecular weight average of the polymer in the oil recoveryformulation should be sufficient to provide sufficient viscosity to theoil recovery formulation to drive petroleum or a mixture of petroleumand the oil recovery formulation through the formation. The polymer mayhave a molecular weight average of at least 10000 daltons, or at least50000 daltons, or at least 100000 daltons. The polymer may have amolecular weight average of from 10000 to 20000000 daltons, or from100000 to 1000000 daltons.

The oil recovery formulation may comprise an alkali. Suitable alkalicompounds include lithium hydroxide, sodium hydroxide, potassiumhydroxide, lithium carbonate, sodium carbonate, potassium carbonate,lithium bicarbonate, sodium bicarbonate, potassium bicarbonate, lithiumsilicate, lithium phosphate, sodium silicate, sodium phosphate,potassium silicate, and potassium phosphate. The oil recoveryformulation may comprise from 0.001 wt. % to 5 wt. % of the alkali, orfrom 0.005 wt. % to 1 wt. % of the alkali, or from 0.01 wt. % to 0.5 wt.% of the alkali.

In one aspect, the present invention is directed to an oil recoveryformulation composition. The oil recovery formulation compositioncomprises a fluid, a surfactant dispersed in the fluid, and asacrificial agent dispersed in the fluid, where the sacrificial agent isselected from the group consisting of a compound comprising a singlecarboxylic acid, carboxylic acid derivative, or carboxylate salt moiety,as described above; a compound comprising a stabilized enol or that isenolizable, as described above; a compound having a molecular weight ofabout 1000 or less comprising one or more hydroxyl groups, as describedabove; a “reducing acid”, as described above; a compound that is acidicor is a salt thereof where the compound lacks a carboxylic acid moiety,a sulfonic acid moeity, a carboxylate salt moiety, or a sulfonate saltmoiety and is selected from the group consisting of a phenol, asulfonamide, a thiol, and combinations thereof. The fluid may be water.The surfactant may be an anionic surfactant, and the anionic surfactantmay be selected from the group consisting of an alpha olefin sulfonatecompound, an internal olefin sulfonate compound, a branched alkylbenzene sulfonate compound, a propylene oxide sulfate compound, or ablend thereof. The oil recovery formulation composition may furthercomprise a polymer selected from the group consisting ofpolyacrylamides, partially hydrolyzed polyacrylamides, polyacrylates,ethylenic co-polymers, biopolymers, carboxymethylcelloluses, polyvinylalcohols, polystyrene sulfonates, polyvinylpyrrolidones, AMPS(2-acrylamide-methyl propane sulfonate), and combinations thereof, asdescribed above. The oil recovery formulation composition may furthercomprise an alkali, as described above. The alkali compound may beselected from the group consisting of lithium hydroxide, sodiumhydroxide, potassium hydroxide, lithium carbonate, sodium carbonate,potassium carbonate, lithium bicarbonate, sodium bicarbonate, potassiumbicarbonate, lithium silicate, lithium phosphate, sodium silicate,sodium phosphate, potassium silicate, potassium phosphate, and mixturesthereof.

The oil recovery formulation composition may contain from 0.001 wt. % to5 wt. %, or from 0.01 wt. % to 0.5 wt. % of the sacrificial agent, asdescribed above, and may contain from 0.05 wt. % to 5 wt. %, or from 0.1wt. % to 3 wt. % of the surfactant as described above, where the balanceof the oil recovery formulation is a fluid in which the sacrificialagent and the surfactant are dispersed, and preferably dissolved, wherethe fluid may be water. The oil recovery formulation composition mayfurther comprise from 250 ppm to 5000 ppm, or from 500 ppm to 2500 ppm,of the polymer, as described above. The oil recovery formulation mayfurther comprise from 0.001 wt. % to 5 wt. %, or from 0.01 wt. % to 0.5wt. % of the alkali, as described above.

In the method of the present invention the oil recovery formulation isintroduced into a petroleum-bearing formation, and the system of thepresent invention includes a petroleum-bearing formation. Thepetroleum-bearing formation comprises petroleum that may be separatedand produced from the formation after contact and mixing with the oilrecovery formulation. The petroleum of the petroleum-bearing formationmay be a heavy oil containing at least 25 wt. %, or at least 30 wt. %,or at least 35 wt. %, or at least 40 wt. % of hydrocarbons having aboiling point of at least 538° C. (1000° F.) as determined in accordancewith ASTM Method D5307. The heavy oil may have an asphaltene content ofat least at least 5 wt. %, or at least 10 wt. %, or at least 15 wt. %,where “asphaltene” as used herein refers to a hydrocarbon compound thatis insoluble in n-heptane and in soluble in toluene. The petroleumcontained in the petroleum-bearing formation may be an intermediateweight oil or a relatively light oil containing less than 25 wt. %, orless than 20 wt. %, or less than 15 wt. %, or less than 10 wt. %, orless than 5 wt. % of hydrocarbons having a boiling point of at least538° C. (1000° F.). The intermediate weight oil or light oil may have anasphaltene content of less than 5 wt. %.

The petroleum contained in the petroleum-bearing formation may have adynamic viscosity under formation conditions (in particular, attemperatures within the temperature range of the formation) of at least1 mPa s (1 cP), or at least 10 mPa s (10 cP), or at least 100 mPa s (100cP), or at least 1000 mPa s (1000 cP), or at least 10000 mPa s (10000cP). The petroleum contained in the petroleum-bearing formation may havea dynamic viscosity under formation temperature conditions of from 1 to10000000 mPa s (1 to 10000000 cP).

The petroleum-bearing formation may be a subterranean formation. Thesubterranean formation may be comprised of one or more porous matrixmaterials selected from the group consisting of a porous mineral matrix,a porous rock matrix, and a combination of a porous mineral matrix and aporous rock matrix, where the porous matrix material may be locatedbeneath an overburden at a depth ranging from 50 meters to 6000 meters,or from 100 meters to 4000 meters, or from 200 meters to 2000 metersunder the earth's surface. The subterranean formation may be a subseasubterranean formation.

The porous matrix material may be a consolidated matrix material inwhich at least a majority, and preferably substantially all, of the rockand/or mineral that forms the matrix material is consolidated such thatthe rock and/or mineral forms a mass in which substantially all of therock and/or mineral is immobile when petroleum, the oil recoveryformulation, water, or other fluid is passed therethrough. Preferably atleast 95 wt. % or at least 97 wt. %, or at least 99 wt. % of the rockand/or mineral is immobile when petroleum, the oil recovery formulation,water, or other fluid is passed therethrough so that any amount of rockor mineral material dislodged by the passage of the petroleum, oilrecovery formulation, water, or other fluid is insufficient to renderthe formation impermeable to the flow of the oil recovery formulation,petroleum, water, or other fluid through the formation. The porousmatrix material may be an unconsolidated matrix material in which atleast a majority, or substantially all, of the rock and/or mineral thatforms the matrix material is unconsolidated. The formation may have apermeability of from 0.0001 to 15 Darcys, or from 0.001 to 1 Darcy. Therock and/or mineral porous matrix material of the formation may becomprised of sandstone and/or a carbonate selected from dolomite,limestone, and mixtures thereof—where the limestone may bemicrocrystalline or crystalline limestone and/or chalk.

Petroleum in the petroleum-bearing formation may be located in poreswithin the porous matrix material of the formation. The petroleum in thepetroleum-bearing formation may be immobilized in the pores within theporous matrix material of the formation, for example, by capillaryforces, by interaction of the petroleum with the pore surfaces, by theviscosity of the petroleum, or by interfacial tension between thepetroleum and water in the formation.

The petroleum-bearing formation may also be comprised of water, whichmay be located in pores within the porous matrix material. The water inthe formation may be connate water, water from a secondary or tertiaryoil recovery process water-flood, or a mixture thereof. The water in thepetroleum-bearing formation may be positioned to immobilize petroleumwithin the pores. Contact of the oil recovery formulation with thepetroleum in the formation may mobilize the petroleum in the formationfor production and recovery from the formation by freeing at least aportion of the petroleum from pores within the formation.

In some embodiments, the petroleum-bearing formation may compriseunconsolidated sand and water. The petroleum-bearing formation may be anoil sand formation. In some embodiments, the petroleum may comprisebetween about 1 wt. % and about 16 wt. % of the oil/sand/water mixture,the sand may comprise between about 80 wt. % and about 85 wt. % of theoil/sand/water mixture, and the water may comprise between about 1 wt. %and about 16 wt. % of the oil/sand water mixture. The sand may be coatedwith a layer of water with the petroleum being located in the void spacearound the wetted sand grains. Optionally, the petroleum-bearingformation may also include a gas, such as methane or air, for example.

Referring now to FIG. 1, a system 200 of the present invention forpracticing a method of the present invention is shown. The systemincludes a first well 201 and a second well 203 extending into apetroleum-bearing formation 205 such as described above. Thepetroleum-bearing formation 205 may be comprised of one or moreformation portions 207, 209, and 211 formed of porous material matrices,such as described above, located beneath an overburden 213. An oilrecovery formulation comprising a fluid, preferably water, a surfactant,and a sacrificial agent as described above, and optionally comprising apolymer and/or an alkali as described above, is provided. The oilrecovery formulation may be provided from an oil recovery formulationstorage facility 215 fluidly operatively coupled to a firstinjection/production facility 217 via conduit 219. Firstinjection/production facility 217 may be fluidly operatively coupled tothe first well 201, which may be located extending from the firstinjection/production facility 217 into the petroleum-bearing formation205. The oil recovery formulation may flow from the firstinjection/production facility 217 through the first well to beintroduced into the formation 205, for example in formation portion 209,where the first injection/production facility 217 and the first well, orthe first well itself, include(s) a mechanism for introducing the oilrecovery formulation into the formation. Alternatively, the oil recoveryformulation may flow from the oil recovery formulation storage facility215 directly to the first well 201 for injection into the formation 205,where the first well comprises a mechanism for introducing the oilrecovery formulation into the formation. The mechanism for introducingthe oil recovery formulation into the formation 205 via the first well201—located in the first injection/production facility 217, the firstwell 201, or both—may be comprised of a pump 221 for delivering the oilrecovery formulation to perforations or openings in the first wellthrough which the oil recovery formulation may be introduced into theformation.

The oil recovery formulation may be introduced into the formation 205,for example by injecting the oil recovery formulation into the formationthrough the first well 201 by pumping the oil recovery formulationthrough the first well and into the formation. The pressure at which theoil recovery formulation is introduced into the formation may range fromthe instantaneous pressure in the formation up to, but not including,the fracture pressure of the formation. The pressure at which the oilrecovery formulation may be injected into the formation may range from20% to 95%, or from 40% to 90%, of the fracture pressure of theformation. Alternatively, the oil recovery formulation may also beinjected into the formation at a pressure of at least the fracturepressure of the formation, where the oil recovery formulation isinjected under fracturing conditions.

The volume of oil recovery formulation introduced into the formation 205via the first well 201 may range from 0.001 to 5 pore volumes, or from0.01 to 2 pore volumes, or from 0.1 to 1 pore volumes, or from 0.2 to0.6 pore volumes, where the term “pore volume” refers to the volume ofthe formation that may be swept by the oil recovery formulation betweenthe first well 201 and the second well 203. The pore volume may bereadily be determined by methods known to a person skilled in the art,for example by modelling studies or by injecting water having a tracercontained therein through the formation 205 from the first well 201 tothe second well 203.

As the oil recovery formulation is introduced into the formation 205,the oil recovery formulation spreads into the formation as shown byarrows 223. Upon introduction to the formation 205, the oil recoveryformulation contacts and forms a mixture with a portion of the petroleumin the formation. The oil recovery formulation may mobilize thepetroleum in the formation upon contacting and mixing with the petroleumand water in the formation. The oil recovery formulation may mobilizethe petroleum in the formation upon contacting and mixing with thepetroleum, for example, by reducing capillary forces retaining thepetroleum in pores in the formation, by reducing the wettability of thepetroleum on pore surfaces in the formation, by reducing the interfacialtension between petroleum and water in the formation, and/or by forminga microemulsion with petroleum and water in the formation.

Upon introduction of the oil recovery formulation into the formation,the sacrificial agent may interact with the formation, the water in theformation, petroleum in the formation and/or the surfactant to inhibitloss of the surfactant within the formation. The sacrificial agent maytemporarily or permanently bind to surfaces within the formation, forexample to mineral or rock surfaces within the formation, and/or thesacrificial agent may temporarily or permanently bind to ions,preferably divalent cations, in the water within the formation toinhibit or prevent the loss of the surfactant within the formation.

The mobilized mixture of the oil recovery formulation and petroleum andany unmixed oil recovery formulation may be pushed across the formation205 from the first well 201 to the second well 203 by furtherintroduction of more oil recovery formulation into the formation. Theoil recovery formulation may be designed to displace the mobilizedmixture of the oil recovery formulation and petroleum through theformation for production at the second well 203. As described above, theoil recovery formulation may contain a polymer, wherein the oil recoveryformulation comprising the polymer may have a viscosity of at least thesame order of magnitude as the viscosity of the petroleum in theformation under formation temperature conditions, and preferably atleast one order of magnitude greater than the viscosity of the petroleumin the formation at formation temperature conditions, so the oilrecovery formulation may drive the mobilized mixture of oil recoveryformulation and petroleum across the formation while inhibitingfingering of the mobilized petroleum/oil recovery formulation throughthe driving plug of oil recovery formulation.

Petroleum may be mobilized for production from the formation 205 via thesecond well 203 by introduction of the oil recovery formulation into theformation, where the mobilized petroleum is driven through the formationfor production from the second well as indicated by arrows 229 byintroduction of the oil recovery formulation into the formation via thefirst well 201. The petroleum mobilized for production from theformation 205 may include the mobilized petroleum/oil recoveryformulation mixture. Water and/or gas may also be mobilized forproduction from the formation 205 via the second well 203 byintroduction of the oil recovery formulation into the formation via thefirst well 201.

After introduction of the oil recovery formulation into the formation205 via the first well 201, petroleum may be recovered and produced fromthe formation via the second well 203. The oil recovery formulation, ora portion thereof, may also be recovered and produced from theformation, optionally in conjunction with the petroleum. Portions of theoil recovery formulation may be recovered separately from other portionsof the oil recovery formulation. For example, the surfactant or thesacrificial agent of the oil recovery formulation may be recoveredseparately from the fluid of the oil recovery formulation, for example,the surfactant may be recovered in the petroleum produced from theformation and not in water that formed a portion of the oil recoveryformulation.

The system of the present invention may include a mechanism located atthe second well for recovering and producing the petroleum from theformation 205 subsequent to introduction of the oil recovery formulationinto the formation, and may include a mechanism located at the secondwell for recovering and producing the oil recovery formulation or aportion thereof and/or gas from the formation subsequent to introductionof the oil recovery formulation into the formation. The mechanismlocated at the second well 203 for recovering and producing thepetroleum, and optionally for recovering and producing the oil recoveryformulation, or a portion thereof, and/or gas may be comprised of a pump233, which may be located in a second injection/production facility 231and/or within the second well 203. The pump 233 may draw the petroleum,and optionally the oil recovery formulation or a portion thereof and/orgas from the formation 205 through perforations in the second well 203to deliver the petroleum, and optionally the oil recovery formulation ora portion thereof and/or gas, to the second injection/productionfacility 231.

Alternatively, the mechanism for recovering and producing thepetroleum—and optionally the oil recovery formulation or a portionthereof and/or gas—from the formation 205 may be comprised of acompressor 234 that may be located in the second injection/productionfacility 231. The compressor 234 may be fluidly operatively coupled to agas storage tank 241 via conduit 236, and may compress gas from the gasstorage tank for injection into the formation 205 through the secondwell 203. The compressor may compress the gas to a pressure sufficientto drive production of petroleum—and optionally the oil recoveryformulation or a portion thereof and/or gas—from the formation via thesecond well 203, where the appropriate pressure may be determined byconventional methods known to those skilled in the art. The compressedgas may be injected into the formation from a different position on thesecond well 203 than the well position at which the petroleum—andoptionally the oil recovery formulation or a portion thereof and/orgas—are produced from the formation, for example, the compressed gas maybe injected into the formation at formation portion 207 while petroleum,oil recovery formulation, and/or gas are produced from the formation atformation portion 209.

Petroleum, optionally in a mixture with the oil recovery formulation ora portion thereof and/or gas may be drawn from the formation 205 asshown by arrows 229 and produced up the second well 203 to the secondinjection/production facility 231. The petroleum may be separated fromthe oil recovery formulation, or a portion thereof, and/or gas in aseparation unit 235 located in the second injection/production facility231 and operatively fluidly coupled to the mechanism 233 for recoveringand producing petroleum and, optionally, the oil recovery formulation,or a portion thereof, and/or gas, from the formation. The separationunit 235 may be comprised of a conventional liquid-gas separator forseparating gas from the petroleum and the oil recovery formulation; anda conventional hydrocarbon-water separator including a demulsificationunit for separating the petroleum from the oil recovery formulation.

The separated produced petroleum may be provided from the separationunit 235 of the second injection/production facility 231 to a petroleumstorage tank 237, which may be fluidly operatively coupled to theseparation unit 235 of the second injection/production facility byconduit 239. The separated gas, if any, may be provided from theseparation unit 235 of the second injection/production facility 231 tothe gas storage tank 241, which may be fluidly operatively coupled tothe separation unit 235 of the second injection/production facility 231by conduit 243.

The separated produced oil recovery formulation may be provided from theseparation unit 235 of the second injection/production facility 231 tothe oil recovery formulation storage unit 215, which may be fluidlyoperatively coupled to the separation unit 235 of the secondinjection/production facility 231 by conduit 245. Alternatively, theseparated oil recovery formulation may be provided from the separationunit 235 of the second injection/production facility 231 to theinjection mechanism 221 via conduit 238 for re-injection into theformation 205 through the first well 201 for further mobilization andrecovery of petroleum from the formation. Alternatively, the separatedoil recovery formulation may be provided from the separation unit 235 toan injection mechanism such as pump 251 in the secondinjection/production facility 231 via conduit 240 for re-injection intothe formation 205 through the second well 203, optionally together withfresh oil recovery formulation.

In an embodiment of a system and a method of the present invention, thefirst well 201 may be used for injecting the oil recovery formulationinto the formation 205 and the second well 203 may be used to producepetroleum from the formation as described above for a first time period,and the second well 203 may be used for injecting the oil recoveryformulation into the formation 205 to mobilize the petroleum in theformation and drive the mobilized petroleum across the formation to thefirst well and the first well 201 may be used to produce petroleum fromthe formation for a second time period, where the second time period issubsequent to the first time period. The second injection/productionfacility 231 may comprise a mechanism such as pump 251 that is fluidlyoperatively coupled the oil recovery formulation storage facility 215 byconduit 253, and optionally fluidly operatively coupled to theseparation units 235 and 259 by conduits 240 and 242, respectively, toreceive produced oil recovery formulation therefrom, and that is fluidlyoperatively coupled to the second well 203 to introduce the oil recoveryformulation into the formation 205 via the second well. The firstinjection/production facility 217 may comprise a mechanism such as pump257 or compressor 258 for production of petroleum, and optionally theoil recovery formulation and/or gas from the formation 205 via the firstwell 201. The first injection/production facility 217 may also include aseparation unit 259 for separating produced petroleum, produced oilrecovery formulation and/or gas. The separation unit 259 may becomprised of a conventional liquid-gas separator for separating gas fromthe produced petroleum and the produced oil recovery formulation; and aconventional hydrocarbon-water separator for separating the producedpetroleum from the produced oil recovery formulation, where thehydrocarbon-water separator may comprise a demulsifier. The separationunit 259 may be fluidly operatively coupled to: the petroleum storagetank 237 by conduit 261 for storage of produced petroleum in thepetroleum storage tank; and the gas storage tank 241 by conduit 265 forstorage of produced gas in the gas storage tank.

The separation unit 259 may be fluidly operatively coupled to the oilrecovery formulation storage facility 215 by conduit 263 for storage ofthe produced oil recovery formulation in the oil recovery formulationstorage facility 215. The separation unit 259 may be fluidly operativelycoupled to either the injection mechanism 221 of the firstinjection/production facility 217 for injecting the produced oilrecovery formulation into the formation 205 through the first well 201or the injection mechanism 251 of the second injection/productionfacility 231 for injecting the produced oil recovery formulation intothe formation through the second well 203 by conduits 242 and 244,respectively.

The first well 201 may be used for introducing the oil recoveryformulation into the formation 205 and the second well 203 may be usedfor producing petroleum and, optionally the oil recovery formulation,from the formation for a first time period; then the second well 203 maybe used for introducing the oil recovery formulation into the formation205 and the first well 201 may be used for producing petroleum, andoptionally the oil recovery formulation, from the formation for a secondtime period; where the first and second time periods comprise a cycle.Multiple cycles may be conducted which include alternating the firstwell 201 and the second well 203 between introducing the oil recoveryformulation into the formation 205 and producing petroleum, andoptionally the oil recovery formulation, from the formation, where onewell is introducing and the other is producing for the first timeperiod, and then they are switched for a second time period. A cycle maybe from about 12 hours to about 1 year, or from about 3 days to about 6months, or from about 5 days to about 3 months.

Referring now to FIG. 2, an array of wells 300 is illustrated. Array 300includes a first well group 302 (denoted by horizontal lines) and asecond well group 304 (denoted by diagonal lines). In some embodimentsof the system and method of the present invention, the first well of thesystem and method described above may include multiple first wellsdepicted as the first well group 302 in the array 300, and the secondwell of the system and method described above may include multiplesecond wells depicted as the second well group 304 in the array 300.

Each well in the first well group 302 may be a horizontal distance 330from an adjacent well in the first well group 302. The horizontaldistance 330 may be from about 5 to about 1000 meters, or from about 10to about 500 meters, or from about 20 to about 250 meters, or from about30 to about 200 meters, or from about 50 to about 150 meters, or fromabout 90 to about 120 meters, or about 100 meters. Each well in thefirst well group 302 may be a vertical distance 332 from an adjacentwell in the first well group 302. The vertical distance 332 may be fromabout 5 to about 1000 meters, or from about 10 to about 500 meters, orfrom about 20 to about 250 meters, or from about 30 to about 200 meters,or from about 50 to about 150 meters, or from about 90 to about 120meters, or about 100 meters.

Each well in the second well group 304 may be a horizontal distance 336from an adjacent well in the second well group 304. The horizontaldistance 336 may be from about 5 to about 1000 meters, or from about 10to about 500 meters, or from about 20 to about 250 meters, or from about30 to about 200 meters, or from about 50 to about 150 meters, or fromabout 90 to about 120 meters, or about 100 meters. Each well in thesecond well group 304 may be a vertical distance 338 from an adjacentwell in the second well group 304. The vertical distance 338 may be fromabout 5 to about 1000 meters, or from about 10 to about 500 meters, orfrom about 20 to about 250 meters, or from about 30 to about 200 meters,or from about 50 to about 150 meters, or from about 90 to about 120meters, or about 100 meters.

Each well in the first well group 302 may be a distance 334 from theadjacent wells in the second well group 304. Each well in the secondwell group 304 may be a distance 334 from the adjacent wells in firstwell group 302. The distance 334 may be from about 5 to about 1000meters, or from about 10 to about 500 meters, or from about 20 to about250 meters, or from about 30 to about 200 meters, or from about 50 toabout 150 meters, or from about 90 to about 120 meters, or about 100meters.

Each well in the first well group 302 may be surrounded by four wells inthe second well group 304. Each well in the second well group 304 may besurrounded by four wells in the first well group 302.

In some embodiments, the array of wells 300 may have from about 10 toabout 1000 wells, for example from about 5 to about 500 wells in thefirst well group 302, and from about 5 to about 500 wells in the secondwell group 304.

In some embodiments, the array of wells 300 may be seen as a top viewwith first well group 302 and the second well group 304 being verticalwells spaced on a piece of land. In some embodiments, the array of wells300 may be seen as a cross-sectional side view of the formation with thefirst well group 302 and the second well group 304 being horizontalwells spaced within the formation.

Referring now to FIG. 3, an array of wells 400 is illustrated. Array 400includes a first well group 402 (denoted by horizontal lines) and asecond well group 404 (denoted by diagonal lines). The array 400 may bean array of wells as described above with respect to array 300 in FIG.3. In some embodiments of the system and method of the presentinvention, the first well of the system and method described above mayinclude multiple first wells depicted as the first well group 402 in thearray 400, and the second well of the system and method described abovemay include multiple second wells depicted as the second well group 404in the array 400.

The oil recovery formulation may be injected into first well group 402and petroleum, and optionally the oil recovery formulation, may berecovered and produced from the second well group 404. As illustrated,the oil recovery formulation may have an injection profile 406, andpetroleum, and optionally the oil recovery formulation, may be producedfrom the second well group 404 having a petroleum recovery profile 408.

The oil recovery formulation may be injected into the second well group404 and petroleum, and optionally the oil recovery formulation, may beproduced from the first well group 402. As illustrated, the oil recoveryformulation may have an injection profile 408, and petroleum, andoptionally the oil recovery formulation, may be produced from the firstwell group 402 having a petroleum recovery profile 406.

The first well group 402 may be used for injecting the oil recoveryformulation and the second well group 404 may be used for producingpetroleum, and optionally the oil recovery formulation, from theformation for a first time period; then second well group 404 may beused for injecting the oil recovery formulation and the first well group402 may be used for producing petroleum, and optionally the oil recoveryformulation, from the formation for a second time period, where thefirst and second time periods comprise a cycle. In some embodiments,multiple cycles may be conducted which include alternating first andsecond well groups 402 and 404 between injecting the oil recoveryformulation and producing petroleum, and optionally the oil recoveryformulation, from the formation, where one well group is injecting andthe other is producing for a first time period, and then they areswitched for a second time period.

To facilitate a better understanding of the present invention, thefollowing examples of certain aspects of some embodiments are given. Inno way should the following examples be read to limit, or define, thescope of the invention.

Example 1

Erythorbic acid was added at 0.1 wt. % concentration to an ASP fluidcontaining 2 wt. % Na₂CO₃, 1.75 wt. % NaCl, 0.48 wt. % of a C₁₂₋₁₃-7PO(propylene oxide) sulfate surfactant, 0.12 wt. % of a C₁₅₋₁₈ internalolefin sulfonate surfactant, and 10 ppm of a non-interacting cobalttracer. The fluid was then passed through a Berea core in the presenceof a formation brine (formation brine: 14.8 g/L NaCl, 0.043 g/L CaCl₂,0.073 g/L MgCl₂) and both in the presence and the absence of petroleum,and the retention of the various fluid components was determined. Acontrol test was performed with a fluid lacking erythorbic acid. FIGS. 4and 5 show illustrative retention plots of various fluid components inthe presence and absence of erythorbic acid, respectively. As shown inFIG. 4, when erythorbic acid was present, the surfactant trailed thetracer only slightly. When erythorbic acid was present, the surfactanttrailed the cobalt tracer by 0.03 pore volumes (PV) in the presence ofpetroleum and by 0.04 PV in the absence of petroleum. This degree ofretention corresponded to 3.6 mg of retained surfactant per 100 g ofcore in the absence of petroleum. In contrast, as shown in FIG. 5, whenerythorbic acid was absent, the surfactant was much more stronglyretained. When erythorbic acid was absent, the surfactant trailed thecobalt tracer by 0.31 PV in the presence of petroleum and by 0.22 PV inthe absence of petroleum. This degree of retention corresponded to 20 mgof retained surfactant per 100 g of core in the absence of petroleum.FIG. 6 shows an illustrative production chart observed in the presenceof erythorbic acid.

Example 2

The effectiveness of ascorbic acid, glucose (monohydrate), EDTA, sodiumacetate, and erythorbic acid as sacrificial agents for inhibitingsurfactant adsorption in sandstone was determined when used in apre-flush solution prior to contacting sandstone with a surfactant. Fourpre-flush solutions were prepared by mixing a brine solution containing14.8 g/L NaCl, 0.043 g/L CaCl₂.2H₂O, and 0.073 g/L MgCl₂.6H₂O with 500ppm of ascorbic acid, glucose (monohydrate), EDTA, and erythorbic acid,respectively, as a sacrificial agent. A fifth pre-flush solution wasprepared by mixing the same brine solution with 183 ppm of sodiumacetate as a sacrificial agent. For each of the pre-flush solutions, aBandera brown sandstone core was flushed with CO₂ to remove air in thecore and then was saturated with a brine solution containing 14.8 g/LNaCl, 0.043 g/L CaCl₂.2H₂O, and 0.073 g/L MgCl₂.6H₂O. The core was theninjected with 3.5 pore volumes of the pre-flush solution followed byinjection of a surfactant slug of 3 pore volumes, where the surfactantslug contained 0.48 wt. % of a C₁₂₋₁₃ ⁷PO (propylene oxide) sulfatesurfactant, 0.12 wt. % of a C₁₅₋₁₈ internal olefin sulfonate surfactant,and 10 ppm of a non-interacting cobalt tracer in an aqueous brinecontaining 3.45 wt. % NaCl. After the injection of the surfactant slug,the core was injected with 3 pore volumes of an aqueous brine containing3.45 wt. % NaCl. A control was also conducted where a Bandera brownsandstone core saturated with a brine solution containing 14.8 g/L NaCl,0.043 g/L CaCl₂.2H₂O, and 0.073 g/L MgCl₂.6H₂O was injected with 3 porevolumes of the surfactant slug as described above followed by 3 porevolumes of aqueous brine containing 3.45 wt. % NaCl with no injection ofa pre-flush solution.

Retention of the surfactant in the core was measured by calculating thedifference in pore volumes after injection of the surfactant betweenobserved cobalt tracer elution (50%) from the core and the observedsurfactant elution (50%) from the core. The calculated surfactant lagand corresponding calculated amount of surfactant adsorbed to the core(wt./wt.) for each pre-flush solution and the control is shown in Table1 below.

TABLE 1 Preflush Surfactant lag (PV) Adsorption (mg/100 g core) Control(no pre-flush) 1.35 97 Erythorbic acid 0.91 54 Ascorbic acid 0.79 51Glucose 1.18 77 EDTA 1.16 77 Na-acetate 1.24 81

As shown in Table 1, all of the sacrificial agent pre-flush solutionsshowed a positive effect for reducing surfactant retention in the corerelative to the control.

The present invention is well adapted to attain the ends and advantagesmentioned as well as those that are inherent therein. The particularembodiments disclosed above are illustrative only, as the presentinvention may be modified and practiced in different but equivalentmanners apparent to those skilled in the art having the benefit of theteachings herein. Furthermore, no limitations are intended to thedetails of construction or design herein shown, other than as describedin the claims below. While systems and methods are described in terms of“comprising,” “containing,” or “including” various components or steps,the compositions and methods can also “consist essentially of” or“consist of” the various components and steps. Whenever a numericalrange with a lower limit and an upper limit is disclosed, any number andany included range falling within the range is specifically disclosed.In particular, every range of values (of the form, “from a to b,” or,equivalently, “from a-b”) disclosed herein is to be understood to setforth every number and range encompassed within the broader range ofvalues. Whenever a numerical range having a specific lower limit only, aspecific upper limit only, or a specific upper limit and a specificlower limit is disclosed, the range also includes any numerical value“about” the specified lower limit and/or the specified upper limit.Also, the terms in the claims have their plain, ordinary meaning unlessotherwise explicitly and clearly defined by the patentee. Moreover, theindefinite articles “a” or “an”, as used in the claims, are definedherein to mean one or more than one of the element that it introduces.

What is claimed is:
 1. A method comprising: providing an oil recoveryformulation comprising a fluid, a surfactant dispersed in the fluid, anda sacrificial agent dispersed in the fluid, wherein the sacrificialagent is selected from the group consisting of a compound comprising asingle carboxylic acid, a single carboxylic acid derivative, or a singlecarboxylate salt; a compound lacking a carboxylic acid group, acarboxylate group, a sulfonic acid group, and a sulfonate group that isa phenol, a sulfonamide, or a thiol; a compound having a molecularweight of 1000 or less and comprising one or more hydroxyl groups; andmixtures thereof; introducing the oil recovery formulation into apetroleum-bearing formation; contacting the oil recovery formulationwith the petroleum-bearing formation and with petroleum in thepetroleum-bearing formation; and producing petroleum from thepetroleum-bearing formation after introducing the oil recoveryformulation into the petroleum-bearing formation.
 2. The method of claim1, wherein the petroleum-bearing formation is a subterranean formation.3. The method of claim 2, wherein the oil recovery formulation isintroduced into the formation via a first well and the petroleum isproduced via a second well.
 4. The method of claim 3, further comprisingproducing at least a portion of the oil recovery formulation from thesecond well.
 5. The method of claim 4, further comprising introducing atleast a portion of the produced oil recovery formulation to thesubterranean formation.
 6. The method of claim 1, wherein the oilrecovery formulation further comprises an alkali and a polymer.
 7. Themethod of claim 6, wherein the polymer is selected from the groupconsisting of polyacrylamides, partially hydrolyzed polyacrylamides,polyacrylates, ethylenic co-polymers, biopolymers,carboxymethylcelloluses, polyvinyl alcohols, polystyrene sulfonates,polyvinylpyrrolidones, AMPS (2-acrylamide-methyl propane sulfonate), andcombinations thereof and the alkali is selected from the groupconsisting of lithium hydroxide, sodium hydroxide, potassium hydroxide,lithium carbonate, sodium carbonate, potassium carbonate, lithiumbicarbonate, sodium bicarbonate, potassium bicarbonate, lithiumsilicate, lithium phosphate, sodium silicate, sodium phosphate,potassium silicate, and potassium phosphate, and mixtures thereof. 8.The method of claim 1, wherein the sacrificial agent comprises amonohydroxycarboxylic acid, a dihydroxycarboxylic acid, atrihydroxycarboxylic acid, a tetrahydroxycarboxylic acid, apentahydroxycarboxylic acid, a salt thereof, or any combination thereof.9. The method of claim 1, wherein the sacrificial agent comprises 10carbons or less.
 10. The method of claim 1, wherein the sacrificialagent comprises an oxidizable functional group.
 11. The method of claim10, further comprising oxidizing the sacrificial agent while contactingthe petroleum-bearing formation.
 12. The method of claim 1, wherein thesacrificial agent comprises an enol.
 13. The method of claim 1, whereinthe sacrificial agent comprises a reductone.
 14. The method of claim 13,wherein the sacrificial agent further comprises a carboxylic acidderivative selected from the group consisting of an ester and an amide.15. The method of claim 14, wherein the sacrificial agent comprises alactone or a lactam.
 16. The method of claim 1, wherein the sacrificialagent comprises a carbohydrate selected from the group consisting of amonosaccharide, a disaccharide, a trisaccharide, a tetrasaccharide, apentasaccharide, or any combination thereof, wherein the carbohydratecomprises at least one reducing sugar.
 17. The method of claim 1,wherein the sacrificial agent is selected from the group consisting oferythorbic acid, ascorbic acid, dehydroerythorbic acid, dehydroascorbicacid, a derivative thereof, or a salt thereof, and any combinationthereof.
 18. The method of claim 1, wherein the sacrificial agentcomprises from 0.001 wt. % to 5 wt. %, or from 0.01 wt. % to 0.5 wt. %of the oil recovery formulation.
 19. The method of claim 1, wherein thesurfactant is an anionic surfactant.
 20. The method of claim 19, whereinthe surfactant is selected from the group consisting of an alpha olefinsulfonate compound, an internal olefin sulfonate compound, a branchedalkyl benzene sulfonate compound, a propylene oxide sulfate compound, ora blend thereof.
 21. The method of claim 1, wherein the surfactantcomprises from 0.05 wt. % to 5 wt. %, or from 0.2 wt. % to 1 wt. % ofthe oil recovery formulation.
 22. The method of claim 1, wherein thefluid of the oil recovery formulation is water or an aqueous brine. 23.A system, comprising: an oil recovery formulation comprising a fluid, asurfactant dispersed in the fluid, and a sacrificial agent dispersed inthe fluid, wherein the sacrificial agent is selected from the groupconsisting of a compound comprising a single carboxylic acid, a singlecarboxylic acid derivative, or a single carboxylate salt; a compoundlacking a carboxylic acid group, a carboxylate group, a sulfonic acidgroup, and a sulfonate group that is a phenol, a sulfonamide, or athiol; a compound having a molecular weight of 1000 or less andcomprising one or more hydroxyl groups; and mixtures thereof; apetroleum-bearing formation; a mechanism for introducing the oilrecovery formulation into the petroleum-bearing formation; and amechanism for producing petroleum from the petroleum-bearing formationsubsequent to introduction of the oil recovery formulation into theformation.
 24. The system of claim 23, wherein the petroleum-bearingformation is a subterranean formation.
 25. The system of claim 24,wherein the mechanism for introducing the oil recovery formulation intothe formation is located at a first well, wherein the first well extendsinto the subterranean formation.
 26. The method of claim 25, wherein themechanism for producing the petroleum from the formation is located at asecond well, wherein the second well extends into the subterraneanformation.
 27. The method of claim 23, wherein the surfactant is ananionic surfactant.
 28. The method of claim 23, wherein the oil recoveryformulation further comprises a polymer.
 29. The system of claim 28,wherein the oil recovery formulation further comprises an alkali. 30.The system of claim 23, wherein the sacrificial agent is selected fromthe group consisting of erythorbic acid, ascorbic acid, a salt thereof,and any combination thereof.